Flexible depth probe

ABSTRACT

An instrument includes a flexible shaft portion and a hook portion. The flexible shaft portion has a proximal end and a distal end and includes markings along an outer surface of the shaft portion. The hook portion is located at the distal end of the shaft portion. The shaft portion and the hook portion define a lumen that terminates in an opening at the hook portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 13/234,636, filed Sep. 16, 2011, entitled “FLEXIBLEDEPTH PROBE,” the entire teachings of all of the above are incorporatedherein by reference as though fully set forth herein.

TECHNICAL FIELD

This document relates to determining bone tunnel depth.

BACKGROUND

An anterior cruciate ligament (ACL) that has ruptured and isnon-repairable is generally replaced arthroscopically by a tissue graft.The tissue graft can be harvested from a portion of a patellar tendonhaving so called “bone blocks” at each end, and from the semitendonosisand gracilis. Alternatively, the tissue graft can be formed fromsynthetic materials or from a combination of synthetic and naturalmaterials. The replacement tissue graft is implanted by securing one endof the tissue graft in a socket formed in a passage within the femur,and passing the other end of the graft through a passage formed in thetibia.

SUMMARY

According to one aspect, an instrument includes a flexible shaft portionand a hook portion. The flexible shaft portion has a proximal end and adistal end and includes markings along an outer surface of the shaftportion. The hook portion is located at the distal end of the shaftportion. The shaft portion and the hook portion define a lumen thatterminates in an opening at the hook portion.

Implementations of this aspect may include one or more of the followingfeatures.

For example, the hook portion may include a tip. The tip may extendbeyond an outer diameter of the flexible shaft portion. The hook portionmay include a chamfer on a surface opposite the tip. The instrument mayfurther include a chamfered connecting portion connecting the hookportion and the flexible shaft portion. The chamfered portion may alsodefine the lumen. The hook portion may include a tip, and the chamferedconnecting portion may include a chamfer along a tip-facing side of thechamfered portion. The shaft portion may include multiple, spaced apartvoids along a length of the shaft portion. The voids may be configuredto provide the shaft with flexibility. The voids may be configured toprovide the shaft with flexibility sufficient to allow the shaft to flexat least 40 degrees without damage. The proximal end of the shaft mayinclude an orientation indicator that indicates the orientation of thehook portion.

According to another aspect, a method of determining a length of a bonetunnel using an instrument includes placing the instrument onto a curvedguide wire that passes through the bone tunnel, moving the instrumentalong the curved guide wire until a hook portion passes through a firstopening of the bone tunnel, through the bone tunnel, and out a secondopening of the bone tunnel, orienting the instrument such that a tip ofthe hook portion substantially faces an outer curvature of the guidewire, retracting the instrument until the hook portion engages acortical surface of the bone, and determining the length of the bonetunnel based on markings along an outer surface of a flexible shaftportion. The instrument includes a flexible shaft portion and a hookportion at a distal end of the shaft.

Implementations of this aspect may include one or more of the followingfeatures.

For example, the shaft portion and the hook portion may define a lumenthat terminates in an opening at the hook portion. Placing theinstrument onto the curved guide wire may include threading the hole andlumen over the guide wire. The instrument may be oriented such that thetip of the hook portion substantially faces an inner curvature of theguide wire while the hook portion passes through the first opening ofthe bone tunnel, through the bone tunnel, and out the second opening ofthe bone tunnel. Orienting the instrument such that the tip of the hookportion substantially faces the outer curvature of the guide wire mayinclude rotating the instrument around the guide wire until the tip ofthe hook portion substantially faces the outer curvature of the guidewire. The method of determining the length of a bone tunnel using theinstrument may include disengaging the hook portion from the corticalsurface, orienting the instrument such that the tip of the hook portionsubstantially faces an inner curvature of the guide wire, and moving thedevice along the curved guide wire until the hook portion passes throughthe second opening of the bone tunnel, through the bone tunnel, and outthe first opening of the bone tunnel. The bone tunnel may be a femoraltunnel. The guide wire may be curved at least 40 degrees such thatmoving the instrument along the curved guide wire causes the flexibleshaft to flex at least 40 degrees. The method of determining the lengthof a bone tunnel using the instrument may include determining anorientation of the hook portion based on an orientation indicator thatindicates the orientation of the hook portion. The orientation indicatormay be located at the proximal end of the shaft.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,aspects, and advantages will become apparent from the description, thedrawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a flexible depth probe.

FIG. 1B is an enlarged perspective view of a hook portion of theflexible depth probe.

FIG. 1C is a partial side view of the flexible depth probe.

FIG. 1D is a cross-sectional view of the probe.

FIG. 1E is a side view of the flexible depth probe.

FIG. 1F is a cross-sectional view of the flexible depth probe of FIG. 1Etaken along the line 1F-1F in the direction of the arrows.

FIG. 1G is a cross-sectional view of the flexible depth probe of FIG. 1Etaken along the line 1G-1G in the direction of the arrows.

FIG. 2A is a side view of the flexible depth probe placed onto a guidewire with a tip of the hook portion facing an inner curvature of theguide wire.

FIG. 2B is a side view of the flexible depth probe placed onto a curvedguide wire with a tip of the hook portion facing an outer curvature ofthe guide wire.

FIGS. 3A-3D illustrate a procedure for forming a femoral tunnel.

FIGS. 4A-4F illustrate a procedure using the flexible depth probe todetermine the depth or length of the femoral tunnel.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

This document describes an example of a flexible depth probe fordetermining the depth or length of a bone tunnel. The flexible depthprobe can, for example, be used to determine the length of a bone tunnelwithin a femur. In some implementations, the flexible depth probe canbend beyond 40 degrees, for example, to 42 degrees.

FIGS. 1A-1G illustrate an example of an implementation of a flexibledepth probe 100. The probe 100 may be used as an instrument, forexample, in determining the length of a bone tunnel in the femur, orfemoral tunnel, during anterior cruciate ligament (ACL) surgery. Theprobe 100 includes a hook portion 102, a flexible shaft portion 104, anda chamfered connecting portion 106. Flexible depth probe 100 defines alumen 110 that starts at the proximal end 118 and terminates in anopening 103 at the distal end 116 (as best seen in FIG. 1B). The overalllength of the flexible depth probe 100 can be, for example, 30 cm. Thediameter of the flexible shaft portion 104 can be 3 mm, and the diameterof lumen 110, which allows a guide wire to fit within it, can be 2.7 mm.The probe wall 109 surrounds the lumen 110 and can be 0.24 mm in wallthickness (as best seen in FIG. 1D). The flexible depth probe 100 can bemade from various materials including, but not limited to, metals andalloys including titanium, stainless steel, anodized aluminum, andnickel titanium (nitinol), as well as different types of plastics andpolymers. In some cases, the flexible depth probe 100 can be made from acombination of different materials.

The flexible shaft portion 104 of depth probe 100 includes multiple,spaced apart voids 108 configured to provide the shaft with flexibility,such that the flexible shaft portion 104 can bend beyond, for example,40 degrees. The spaced apart voids 108 are in the form of slices cutinto alternating sides of the flexible shaft portion 104. The slices canbe 0.3 mm in width and can be spaced 2 mm apart from each other. Thespaced apart voids 108 can alternatively, or additionally, be in theform of a continuous spiral cut, interlocking cut, puzzle cut, or otherappropriate cut arrangement that provides the shaft with flexibility andcan be formed, for example, through electric discharge machining (EDM)or laser cutting. Alternatively, or additionally, inherent flexibilityof the material used in constructing the flexible shaft portion 104, forexample nitinol, can provide flexibility to the section.

Hook portion 102 has a tip 102 a configured to engage or latch onto acortical surface of the bone and a chamfer 112, on the side opposite thetip 102 a, configured to allow the depth probe 100 to slide smoothlyinside, for example, a bone tunnel without damaging the tunnel wall. Thechamfer 112 forms an angle A of, for example, 35 degrees, or moregenerally about 20 to about 85 degrees, with respect to the longitudinalaxis 101 of the depth probe 100 and can be, for example, 4.4 mm inlength when viewed from the side. A lower portion of the opening 103includes a semi-cylindrical portion while the chamfer 112 defines anupper curved portion of the opening 103 (as best seen in FIG. 1B), thelower and upper portions of opening 103 defining a circular perimeteraround longitudinal axis 101 when viewed axially from the distal end116. Alternatively, or additionally, the opening 103 may be entirelycylindrical. The chamfer 112 may or may not expose the interior lumen110. The chamfer 112 may be replaced with a radius in some cases.

The tip 102 a is in the shape of an oblique semi-cylinder. The distalface 113 and the proximal face 111 of the semi-cylinder are angledtowards the proximal end 118. The distal face 113 is angled to help thehook portion 102 slide into the bone tunnel. The proximal face 111 isangled to help the tip 102 a more easily latch onto the cortical surfaceof the bone. Alternatively, or additionally, the tip 102 a can betextured or include additional materials, such as rubber, to more easilyengage the cortical surface. The tip 102 a can further be in the shapeof other geometric forms, such as spheres, prisms, and pyramids, thatallow the tip 102 a to latch onto the cortical surface of the bone. Asshown in FIGS. 1C-1G, the outermost surface of the tip 102 a extendsbeyond the outer surface of the flexible shaft portion 104, for example,by 6 mm, and the proximal face of tip 102 a forms an angle B, forexample, of 110 degrees with respect to the longitudinal axis 101.

The chamfered connecting portion 106 connects the hook portion 102 tothe flexible shaft portion 104 and includes a chamfer 107 along the sameside as the tip 102 a. The chamfered connecting portion 106 isconfigured to provide a smooth transition between the interface region115 and the outer surface of the flexible shaft portion 104. The chamfer107 can from an angle C of about 1 to about 30 degrees with respect tothe longitudinal axis 101 of the depth probe 100 and can be, forexample, 15 mm in length. The chamfer 107 may expose the interior lumen110. As described further below, the chamfer 107 can provide a moresecure engagement of the hook portion 102 to the cortical surface of thebone.

The orientation indicator 120 located proximal to the flexible shaftportion 104 indicates the rotational orientation of the hook portion 102around the longitudinal axis 101 and can be, for example, a straightline 20 mm in length running parallel to longitudinal axis 101 on theside of the flexible depth probe 100 opposite the tip 102 a. Markings114 are placed along the outer surface of the flexible depth probe 100to indicate the length of the object, for example a bone tunnel, and caninclude a plurality of numerical as well as line markings. The numericalmarkings indicate the distance along the outer wall of the flexibleshaft portion 104, on the side of the tip 102 a and the chamfer 107,between the interface region 115 and the respective numerical marking.The numerical markings can be placed every 10 mm on the same and/oropposite side of 102 a. The line markings can be placed every 2 mm andcan run along the entire circumference of the probe 100 at each markinglocation. Alternatively, or additionally, the spaced apart voids 108 canserve as the line markings.

In another implementation, numerical markings can be located furtherproximally, by a known distance, on the flexible depth probe 100 inrelation to their corresponding line markings such that the distancealong the outer wall of flexible shaft portion 104 may be determined byobserving the numerical markings that are located further downproximally. The orientation indicator 120 and markings 114 can bepainted or engraved using a variety of techniques, for example laseretching.

FIGS. 2A-2B show side views of the flexible depth probe 100 placed ontoa guide wire 200. The guide wire 200 is generally straight and can bebent, reversibly or irreversibly, to a desired curvature. The guide wire200 can be made from any appropriate materials, such as, but not limitedto, materials used in making the flexible depth probe 100. Additionally,the guide wire 200 can be an existing guide wire or passing pin of aflexible drill system, such as the Clancy Flexible System by Smith &Nephew.

The guide wire 200 slidably fits within the lumen 110 of the flexibledepth probe 100, as best seen in FIGS. 2A-2B. The length of the guidewire 200 can be 34 cm, and its diameter can be 2.4 mm. As the flexibledepth probe 100 is inserted or threaded over the guide wire 200, theflexibility of the flexible shaft portion 104 allows the shaft portion104 to conform to the shape of guide wire 200. For example, if the guidewire 200 is curved at least 40 degrees, moving the flexible depth probe100 along the curved guide wire 200 causes the flexible shaft portion104 of the depth probe 100 to flex at least 40 degrees. FIG. 2A showsthe flexible depth probe 100 slidably threaded over the guide wire 200and oriented such that the tip 102 a of the hook portion 102 faces aninner curvature 202 of the guide wire 200. As described further below,this rotational orientation of the flexible depth probe 100 can be usedfor insertion into, for example, a femoral tunnel. By rotating theproximal end 118 of the flexible depth probe 100 with respect to theguide wire 200, the entire flexible depth probe 100, including the hookportion 102, rotates in a corresponding manner around the guide wire200. FIG. 2B shows the flexible depth probe 100 slidably threaded overthe guide wire 200 and rotated around the guide wire 200 such that thetip 102 a of the hook portion 102 faces an outer curvature 204 of theguide wire 200. As described further below, this rotational orientationof the flexible depth probe 100 can be used for engaging or latchingonto, for example, the cortical surface of a bone.

FIGS. 3A-3D illustrate a process for drilling a femoral tunnel 306 in afemur 300 via, for example, an anteromedial portal (not shown). Thediameter of the femoral tunnel can be 9 mm and is larger than thelargest diameter found along the hook portion 102. Referring to FIG. 3A,with the patient's knee bent to approximately 90 degrees, a curvedendoscopic femoral guide 302 is introduced through the anteromedialportal. With the femoral guide 302 in position, the guide wire 200(which may also be referred to as a drill tip passing pin) is insertedthrough the femoral guide 302 and advanced through the femur 300 (asbest seen in FIGS. 3A-3B) and, in some cases, through the skin. Due toaxial misalignment between an entry point into the anteromedial portaland a first femoral opening 308, the guide wire 200 is curved beyond 40degrees in most cases. At this point in the process, the femoral guide302 is removed, leaving the guide wire 200 in place.

Referring to FIGS. 3C-3D, a flexible cannulated drill 304 is insertedover the guide wire 200 and advanced until the desired depth of thefemoral tunnel 306 is achieved. The shape of the resulting femoraltunnel 306 follows the trajectory of the guide wire 200 and is generallystraight. Additionally, the femoral tunnel 306 terminates in a secondfemoral opening 310 on the opposite side of the femur 300. The guidewire 200 may or may not extend beyond the second femoral opening 310.

After drilling the femoral tunnel 306 and removing the flexiblecannulated drill 304, as shown in FIG. 3D, the guide wire 200 will tryto straighten out by springing back, in the direction of its outercurvature 204, to its initial shape. This will result in a convex sideof the flexible depth probe 100 coming in contact with an interior wallof the bone tunnel 306. In some cases, the convex side of the probe 100may come in contact with the interior wall of the bone tunnel 306regardless of the shape of the guide wire 200 within the femoral tunnel306.

Referring to FIGS. 4A-4F, the flexible depth probe 100 is used todetermine the length of the femoral tunnel 306. In some cases, the guidewire 200 remains in place following the drilling steps outlined in FIGS.3A-3D. Alternatively, the guide wire 200 may be replaced with anotherguide wire or repositioned within the bone tunnel prior to the depthdetermining step. Due to axial misalignment between the anteromedialportal, where the guide wire 200 first enters the patient's body, andthe first femoral opening 308, where the guide wire 200 first enters thefemur 300, the guide wire 200 can be curved beyond 40 degrees.

As shown in FIG. 4A, the flexible depth probe 100 is threaded over theguide wire 200 and advanced into the femoral tunnel 306 through thefirst femoral opening 308. By observing the orientation indicator 120,which may be inside or outside of the patient's body, the rotationalorientation of the flexible depth probe 100 can be controlled such thatthe tip 102 a of the hook portion 102 substantially faces the innercurvature 202 of the guide wire 200. Due to the tendency of the guidewire 200 and/or the flexible depth probe 100 to straighten out while ina curved state, the probe 100 will tend to push out towards thedirection of the outer curvature 204 and make contact with the interiorwall of the femoral tunnel 306. Because of the chamfer 112, the hookportion 102 is able to pass through the first femoral opening 308without getting stuck and is further able to slide smoothly within thefemoral tunnel 306 without snagging on or damaging the interior wall ofthe femoral tunnel 306. Additionally, because the diameter of thefemoral tunnel is larger than the largest diameter found along the hookportion 102, the tip 102 a of the hook portion 102 will not come incontact with the interior wall of the femoral tunnel 306. As shown inFIG. 4B, the flexible depth probe 100 is advanced until the hook portion102 comes out of the femoral tunnel 306 through the second femoralopening 310.

FIGS. 4C-4F illustrate the process by which the tip 102 a latches on tothe cortical surface of the bone 400. After the hook portion 102 isadvanced past the second femoral opening 310, the proximal end 118 ofthe flexible depth probe 100 is rotated by approximately 180 degreesaround the guide wire 200, as indicated by arrow D in FIG. 4C. As aresult, the hook portion 102 rotates approximately 180 degrees about theguide wire 200, and the tip 102 a substantially faces the outercurvature 204 of the guide wire 200. Due to the tendency of the guidewire 200 and/or the flexible depth probe 100 to straighten out while ina curved state, the probe 100 will tend to push out towards thedirection of the outer curvature 204 and make contact with the interiorwall of the femoral tunnel 306. Because of the chamfer 107, the rotationof the flexible depth probe 100 may cause the hook portion 102 to moveradially outwards in the direction of the outer curvature 204. Thisoutward movement can provide a more secure engagement of the hookportion 102 to the cortical surface of the bone 400 by maximizing theamount of cortical surface 400 that is engaged by the tip 102 a. Oncethe tip 102 a substantially faces the outer curvature 204 of the guidewire 200, the proximal end 118 is retracted in the direction indicatedby arrow E in FIG. 4D. This pulling action causes the tip 102 a toengage or latch onto the cortical surface of the bone 400. Once thecortical surface of the bone 400 has been engaged by the hook portion102, the distance between the interface region 115 and a marking 114adjacent the first femoral opening 308 indicates the length of thefemoral tunnel 306.

The above-mentioned features of the flexible depth probe 100 may enableeasy removal of the probe 100 from the femoral tunnel 306 after a lengthhas been determined, for example, by reversing the order of stepsindicated in FIGS. 4A-4D. The hook portion 102 is disengaged from thecortical surface of the bone 400, for example, by pushing the proximalend 118 of the probe 100 in a direction opposite the direction indicatedby arrow E. Once the hook portion 102 has been disengaged from thecortical surface 400, rotating the proximal end 118 of the probe 100 byapproximately 180 degrees results in the hook portion 102 rotating byapproximately 180 degrees and substantially facing the inner curvature202 of the guide wire 200. Because of the tendency of the guide wire 200to straighten out, the convex side of the probe 100 will push againstthe inner wall of the femoral tunnel 306. At this point in the process,the proximal end 118 of the probe 100 is pulled until the hook portion102 of the probe 100, moving along the guide wire 200, passessequentially through the second femoral opening 310, the femoral tunnel306, the first femoral opening 308, and eventually out of the patient'sbody. Since the diameter of the femoral tunnel 306 is larger than thelargest diameter of the hook portion 102, the tip 102 a of the hookportion 102 will not snag on or damage the interior wall of the femoraltunnel 306.

While this document contains many specific implementation details, theseshould not be construed as limitations on the scope of anyimplementations or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularimplementations. Certain features that are described in this document inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination. Thus, particularimplementations of the subject matter have been described. Otherimplementations are within the scope of the following claims.

The invention claimed is:
 1. A measurement instrument comprising: aflexible shaft portion having a proximal end and a distal end, theflexible shaft portion including measurement markings along an outersurface of the flexible shaft portion; and a hook portion at the distalend of the flexible shaft portion; wherein the flexible shaft portionand the hook portion define a lumen that terminates in an opening at thehook portion, wherein the flexible shaft portion includes multiple,spaced apart voids along a length of the flexible shaft portion, thevoids configured to provide the flexible shaft portion with flexibility,wherein the hook portion includes a tip extending radially outwardbeyond an outer diameter surface of the flexible shaft portion and aterminal end of the hook portion furthest from the flexible shaftportion angled relative to the tip in a direction back towards theproximal end of the shaft, wherein the tip and terminal end aresubstantially coplanar with respect to a plane parallel to alongitudinal axis of the shaft, and wherein a portion of an innerengagement surface of the hook extends back toward a proximal portion ofthe shaft at an acute angle relative to the shaft.
 2. The instrument ofclaim 1, wherein the hook portion includes a first chamfer cutaway, thefirst chamfer cutaway disposed on a surface of the flexible shaftportion opposite the tip; and wherein the hook portion includes a secondchamfer cutaway on the tip opposite the first chamfer cutaway.
 3. Theinstrument of claim 1 further comprising a chamfered connecting portionconnecting the hook portion and the flexible shaft portion, thechamfered connecting portion also defining a lumen.
 4. The instrument ofclaim 3 wherein the chamfered connecting portion includes a chamferalong a tip-facing side of the chamfered connecting portion.
 5. Theinstrument of claim 3, wherein the flexible shaft portion includes anorientation marking indicating a rotational orientation of the flexibleshaft portion, the orientation marking aligning with the chamferedconnecting portion.
 6. The instrument of claim 1 wherein the voids areconfigured to provide the flexible shaft portion with flexibilitysufficient to allow the flexible shaft portion to flex at least 40degrees without damage.
 7. The instrument of claim 1, wherein themultiple spaced apart voids are slices cut into alternating sides of theshaft portion.
 8. The instrument of claim 7, wherein the multiple spacedapart voids includes a first void and a second void disposed on aparticular side of the shaft portion; wherein the markings aremeasurement marking including a first measurement marking and a secondmeasurement marking; and wherein the first measurement marking isdisposed on the side of the shaft between the first void and the secondvoid.
 9. The instrument of claim 1, wherein the shaft includes anorientation marking indicating a rotation orientation of the shaft. 10.The instrument of claim 1, wherein the angling of the terminal end ofthe hook portion relative to the tip defines a cavity.
 11. Theinstrument of claim 10, wherein the hook portion includes a chamferedcutaway on a surface of the flexible shaft portion opposite the tip, thechamfered cutaway on the surface of the flexible shaft portion oppositethe tip exposing the lumen on a side wall along an axial length of theflexible shaft portion.
 12. The instrument of claim 11, wherein thecavity includes a chamfered connecting portion connecting the hookportion and the flexible shaft portion, the chamfered connection portionin the cavity providing an opening to the lumen.
 13. The instrument ofclaim 12, wherein the flexible shaft portion includes multiplespaced-apart voids along a length of the flexible shaft portion, themultiple spaced-apart voids configured to provide the flexible shaftportion with flexibility.
 14. The instrument of claim 13, wherein theproximal end of the flexible shaft portion includes an orientationindicator that indicates a rotational orientation of the tip disposed onthe hook portion.
 15. The instrument of claim 14, wherein the proximalend of the flexible shaft portion includes an outer circumferentialsurface region on which the orientation indicator resides.
 16. Ameasurement instrument comprising: a flexible shaft portion having aproximal end and a distal end, the flexible shaft portion includingmeasurement markings along an outer surface of the flexible shaftportion; a hook portion at the distal end of the flexible shaft portion;wherein the flexible shaft portion and the hook portion define a lumenthat terminates in an opening at the hook portion; wherein the hookportion includes a tip, the tip extending radially outward beyond anouter diameter surface of the flexible shaft portion, a terminal end ofthe hook portion furthest from the flexible shaft portion angled in adirection back towards the proximal end to form a cavity; wherein thehook portion includes a chamfered cutaway on a surface of the flexibleshaft portion opposite the tip, the chamfered cutaway on the surface ofthe flexible shaft portion opposite the tip exposing the lumen on a sidewall along an axial length of the flexible shaft portion; wherein thecavity includes a chamfered connecting portion connecting the hookportion and the flexible shaft portion, the chamfered connection portionin the cavity providing an opening to the lumen; and wherein theproximal end of the flexible shaft portion includes an orientationindicator that indicates a rotational orientation of the hook portiondisposed on the distal end of the flexible shaft portion.
 17. A methodof determining a length of a bone tunnel in a respective bone using ameasurement instrument that includes a flexible shaft portion and a hookportion at a distal end of the flexible shaft portion, the methodcomprising: placing the instrument into a curved guide wire that passesthrough the bone tunnel; moving the flexible shaft portion of theinstrument along the curved guide wire until the hook portion passesthrough a first opening of the bone tunnel, through the bone tunnel, andout a second opening of the bone tunnel; orienting the flexible shaftportion of the instrument such that a tip of the hook portion faces anouter curvature of the guide wire; maintaining the orientation of theflexible shaft portion with the tip of the hook portion facing the outercurvature of the guide wire while retracing the instrument until the tipof the hook portion facing the outer curvature of the guide wire engagesa cortical surface of the respective bone; and determining the length ofthe bone tunnel based on measurement markings along an outer surface ofthe flexible shaft portion.
 18. The method of claim 17 wherein theflexible shaft portion and the hook portion define a lumen thatterminates in an opening at the hook portion; and wherein placing theinstrument into the curved guide wire includes threading the opening andlumen over the guide wire.
 19. The method of claim 17 wherein theinstrument is oriented such that the tip of the hook portion faces aninner curvature of the guide wire while the hook portion passes throughthe first opening of the bone tunnel, through the bone tunnel, and outthe second opening of the bone tunnel.
 20. The method of claim 17wherein orienting the instrument such that the tip of the hook portionfaces the outer curvature of the guide wire includes rotating theinstrument around the guide wire until the tip of the hook portion facesthe outer curvature of the guide wire.
 21. The method of claim 17further comprising: disengaging the hook portion from the corticalsurface; orienting the instrument such that the tip of the hook portionfaces an inner curvature of the guide wire; and moving the instrumentalong the curved guide wire until the hook portion passes through thesecond opening of the bone tunnel, through the bone tunnel, and out thefirst opening of the bone tunnel.
 22. The method of claim 17 furthercomprising determining an orientation of the hook portion based on theorientation indicator that indicates the orientation of the hookportion, the orientation indicator being located at a proximal end ofthe flexible shaft portion.
 23. The method as in claim 17, wherein theflexible shaft portion has a tendency to straighten out, facilitatingengagement of the tip of the hook portion with the cortical surface ofthe respective bone.
 24. The method as in claim 17, wherein the bonetunnel has a larger diameter than a diameter of the hook portiondisposed at the distal end of the flexible shaft portion.
 25. The methodas in claim 23 further comprising: orientating the flexible shaftportion such that a tip of the hook portion faces an inner curvature ofthe guide wire to disengage the tip of the hook portion from thecortical surface of the bone; and retracting the flexible shaft portionfrom the bone tunnel.